1. Field of the Invention
The present invention relates to telecommunications, and more particularly, to wireless communications.
2. Background Art
A wireless telecommunications network is typically made up of a plurality of wireless devices forming point-to-point, multi-point or broadcast radio systems each using a set of frequencies to establish forward links and reverse links for bidirectional communications. A typical point-to-point radio system with two wireless devices capable of handling bidirectional communications traffic is illustrated in the diagram of FIG. 1. In FIG. 1, a first wireless device 2 comprises a radio frequency (RF) transmitter 4 and an RF receiver 6, while a second wireless device 8 comprises an RF transmitter 10 and an RF receiver 12. The RF transmitters and receivers in the wireless devices are capable of transmitting and receiving radio frequency signals at frequencies in one or more frequency bands.
When the transmitter 4 of the wireless device 2 transmits RF signals in a selected frequency channel, the receiver 12 in the second wireless device 8 need be tuned to that frequency channel to receive the RF signals transmitted by the transmitter 4 of the first wireless device 2. Similarly, the RF receiver 6 in the first wireless device 2 need be tuned to the frequency channel used by the transmitter 10 of the second wireless device 8. A frequency channel is usable for communications between the two wireless devices if it is permitted by government regulations, for example, regulations by the Federal Communications Commission (FCC) in the United States, and if the reception of RF signals is not significantly degraded by the presence of excessive external or local noise at the receivers of the wireless devices.
Bidirectional communications between two wireless devices in a point-to-point radio system may be characterized by either a simplex link or a full duplex link. In a simplex link, RF signals on the radio signal path 14 from the first wireless 2 to the second wireless device 8 and RF signals on the radio signal path 16 from the second wireless device 8 to the first wireless device 2 as illustrated in FIG. 1 utilize the same frequency at different times. In order to avoid interference in bidirectional communications utilizing the same frequency channel, internal or external means which are well known to a person skilled in the art are typically used to prevent simultaneous transmissions in conventional point-to-point radio systems with simplex links.
In a full duplex link, RF signals on the radio signal path 14 from the first wireless device 2 to the second wireless device 8 are transmitted using a frequency channel different from that which is used for the transmission of RF signals from the second wireless device 8 to the first wireless device 2 along the radio signal path 16. The frequency separation between the transmit frequencies of these two wireless devices is based upon various factors including, for example, the filtering and rejection capability of duplexers in the wireless devices, antenna separation if the transmit antenna is separate from the receive antenna of each wireless device, and digital signal processing capabilities of the wireless devices.
In a typical wideband full duplex system, two independent channels, each of a continuous bandwidth, are used to transmit signals between two wireless devices. The bandwidth of these channels can range from tens of kilohertz to hundreds of megahertz, and possibly very well into a gigahertz range in a very wide band RF system. In a typical wideband full duplex system, the spectral locations of the transmit and receive channels for each of the wireless devices are usually determined by a combination of factors, including government regulations and practical considerations.
If a radio system is used for operations in one or more unlicensed radio bands, wide segments of the radio bands may be allocated for general operations if no interference is present in these bands. The unlicensed bands are in turn subdivided into individual transmit and receive channels. In a typical scenario, the individual transmit and receive channels are allocated base upon an a priori determination of frequency separation required to reduce self-interference between the transmitters and receivers of wireless devices.
Because of predetermined frequency channel allocation, wireless devices in conventional radio systems are not afforded the capability of dynamically selecting open channels by finding and using locally non-interfering band segments within a larger allocated band for establishing and maintaining bidirectional radio communications. It is typical that the noise signature for a given frequency band may vary from time to time. Furthermore, it is typical in an unlicensed radio band that a frequency channel may be clear and available at a given time but occupied by another communications link at another time.
Therefore, there is a need for a method of establishing and maintaining communications links between wireless devices by adaptively setting frequency channels in one or more frequency bands in a wireless communications network with point-to-point, multi-point or broadcast links.